Future Technology Devices Intl Ltd. Application Note. FT232BM and FT245BM Power Control and Pin States

Transcription

1 Future Technology Devices Intl Ltd. Application Note FT232BM and FT245BM Power Control and Pin States Created by Future Technology Devices Intl. ( FTDI ) Ltd. Contents Copyright (c) 2003 / 2004 FTDI Ltd.

2 I FT232BM and FT245BM Power Control and Pin States Table of Contents Part 1 FT232BM and FT245BM Power Control Introduction... 1 Part 2 Pin States FT232BM Pin States FT245BM Pin States

3 FT232BM and FT245BM Power Control and Pin States 1 1 FT232BM and FT245BM Power Control 1.1 Introduction FT232BM and FT245BM Power Control / Pin States Background USB Bus Powered peripherals ( ones that get their power from the USB bus ) have a number of restrictions that can make it difficult for a design to meet the mandatory USB 2.0 requirements. Failure to meet these requirements can result in unreliable operation under certain conditions, also a peripheral that does not meet these requirements will fail the USB certification process and will not be eligible to use the USB Certified logo on the product packaging and marketing. The requirements in question are - In USB suspend mode, a Bus Powered USB peripheral must draw no more than 0.5mA ( 500uA ) from the USB bus NOTE : The 500uA suspend current limit includes the 200uA current draw of the 1.5k pull-up on the USB D+. This leaves only 300uA ( 0.3mA ) to power the FT232BM / FT245BM and the external peripheral circuitry. On power-up a Bus Powered USB peripheral may draw no more than 100mA from the USB bus until the device has been successfully enumerated ( drivers loaded and ready to go ) by the Host PC. NOTE : USB Bus Powered peripherals may draw up to 500mA current from the USB bus after enumeration, unless they are plugged into a Bus Powered USB Hub in which case the limit is 100mA only. In order to substantially reduce the effort and cost of meeting these requirements, FTDI have incorporated two new features in their BM series devices which if used correctly make designing such USB Bus Powered peripheral designs straight forward. Firstly, the BM series devices have a PWREN# pin which can be used to control the power to external logic using a low cost power P-Channel MOSFET. Examples of how to implement such a circuit are provided in the FT232BM / FT245BM version 2.0 schematics and designer guides which can be downloaded from the FTDI site. Secondly, the BM series devices have a pull-down mode ( PDEN ) where the peripheral interface pins are pulled down when the PWREN# pin is high ( power = off ). The pulldown resistors are used to bleed any residual voltages in the external circuitry to GND and to eliminate any stray leakage from the external circuitry through to the USB supply

4 2 FT232BM and FT245BM Power Control and Pin States voltage, thus reducing supply current from the USB bus to a minimum during USB suspend. To enable this mode, the BM series device must have an external configuration EEPROM connected and the Pull-Down mode must be set in the EEPROM configuration data. NOTE : The FT232BM and FT245BM devices have both pull-up and pull-down resistors on their peripheral interface pins. These default to pulling input pins high unless pull-down mode is enabled in the configuration EEPROM and PWREN# is high. PWREN# states The PWREN# signal will be high ( power = off ) under the following conditions - The FT232BM / FT245BM device is in reset OR The FT232BM / FT245BM device is not yet configured by USB enumeration, or the USB enumeration sequence has failed OR The host PC system is in the USB suspend state Pull Up / Pull Down Values The Pull Up and Pull Down resistors have a nominal value of 200 KOhm with a tolerance of +/- 50%. This gives possible values of K Ohm. Interface Pins - IO Voltage All the peripheral interface IO pins are powered from the VCCIO pin 13 of the FT232BM and FT245BM. If the VCCIO pin is connected to 3.3 volts then these pins will drive to 3.3 volts. This makes it simple to connect to 3.3 volt logic. The interface pins powered by VCCIO are... FT232BM - TXD, RXD, RTS#, CTS#, DTR#, DSR#, DCD#, RI#, TXDEN, PWREN#, PWRCTL, TXLED, RXLED, SLEEP# FT245BM - D[0...7], RD#, WR, TXE, RXF#, SI/WU, PWREN# EEPROM Interface Pins The pins EESK, EECS, and EEDATA operate at 5 volt levels only. These pins will be tristate, but pulled high via an internal 200 K Ohm (+/-50%) resistor during device reset. RESET#, RSTOUT# and TEST

5 FT232BM and FT245BM Power Control and Pin States 3 TEST, RESET#, and RSTOUT# operate at 5 volt levels only. RSTOUT# is driven low during device reset. Interface Pins - Bit Bang Mode In addition to the usual pin states, the FT232BM and FT245BM peripheral interfaces can be configured ( via a USB command ) into a further mode known as Bit Bang mode - effectively acting as a general purpose IO port until switched back into the native mode of the device. The behaviour of the pull-up/ pull-down resistors in Bit Bang mode may differ from the native mode of the device, so the pins states for this mode are also defined in this document.

6 4 FT232BM and FT245BM Power Control and Pin States 2 Pin States 2.1 FT232BM Pin States int PDEN off int PDEN on Pin PWREN# off PWREN# on PWREN# off PWREN# on Bit Bang Mode TXD O/P O/P I/P with PD O/P PU if I/P RXD I/P with PU I/P with PU I/P with PD I/P with PU PU if I/P RTS# O/P O/P I/P with PD O/P PU if I/P CTS# I/P with PU I/P with PU I/P with PD I/P with PU PU if I/P DTR# O/P O/P I/P with PD O/P PU if I/P DSR# I/P with PU I/P with PU I/P with PD I/P with PU PU if I/P DCD# I/P with PU I/P with PU I/P with PD I/P with PU PU if I/P RI# I/P with PU I/P with PU I/P with PD I/P with PU PU if I/P TXDEN O/P O/P O/P O/P O/P '0' PWREN# O/P '1' O/P '0' O/P '1' O/P '0' I/P PWREN# PWRCTL I/P with PU I/P with PU I/P with PU I/P with PU I/P with PU TXLED I/P no PU I/P no PU (1) I/P with PU I/P no PU (1) I/P with PU RXLED I/P no PU I/P no PU (1) I/P with PU I/P no PU (1) I/P with PU SLEEP# O/P O/P O/P O/P O/P SLEEP# (1) :- These are input unless they are signalling an RX or TX character. When they are signalling they switch to output driving '0'. key : PD - Pull Down resistor PU - Pull Up resistor O/P - Output with no pull up or pull down resistor I/P - Input I/O - input or output depending on FT245BM RD# line int PDEN - bit held in EEPROM set using FTD2XXST.exe programmer. PWREN# off - off if chip is held reset OR it is NOT configured OR it is in suspend. PWREN# on - on if chip is NOT held reset AND it is configured AND it is NOT in suspend. Bit Bang Mode - this overrides the 'int PDEN ' bit set by the EEPROM.

7 FT232BM and FT245BM Power Control and Pin States FT245BM Pin States int PDEN off int PDEN on Pin PWREN# off PWREN# on PWREN# off PWREN# on Bit Bang Mode D0 I/O with PU I/O with PU I/P with PD I/O with PU PU if I/P D1 I/O with PU I/O with PU I/P with PD I/O with PU PU if I/P D2 I/O with PU I/O with PU I/P with PD I/O with PU PU if I/P D3 I/O with PU I/O with PU I/P with PD I/O with PU PU if I/P D4 I/O with PU I/O with PU I/P with PD I/O with PU PU if I/P D5 I/O with PU I/O with PU I/P with PD I/O with PU PU if I/P D6 I/O with PU I/O with PU I/P with PD I/O with PU PU if I/P D7 I/O with PU I/O with PU I/P with PD I/O with PU PU if I/P RD# I/P with PU I/P with PU I/P with PD I/P with PU I/P with PU WR I/P with PU I/P with PU I/P with PD I/P with PU I/P with PU TXE# O/P (2) O/P (2) I/P with PD O/P O/P '1' (2) RXF# O/P (2) O/P (2) I/P with PD O/P O/P '1' (2) SND/Wake I/P with PU I/P with PU I/P with PD I/P with PU (2)I/P with PU PWREN# O/P '1' O/P '0' O/P '1' O/P '0' O/P '0' (2) :- These become I/P with PU if the chip is in suspend. key : PD - Pull Down resistor PU - Pull Up resistor O/P - Output with no pull up or pull down resistor I/P - Input I/O - input or output depending on FT245BM RD# line int PDEN - bit held in EEPROM set using FTD2XXST.exe programmer. PWREN# off - off if chip is held reset OR it is NOT configured OR it is in suspend. PWREN# on - on if chip is NOT held reset AND it is configured AND it is NOT in suspend. Bit Bang Mode - this overrides the 'int PDEN ' bit set by the EEPROM.

8 6 Index - B - Background 1 - F - FT232BM - Pin States 4 FT245BM - Pin States 5 - I - Interface Pins - Bit Bang Mode 1 Interface Pins - IO Voltage 1 Introduction 1 - P - Pin States - FT232BM 4 Pin States - FT245BM 5 Pull Up / Pull Down Values 1 PWREN# states 1